Valerie Macon/Getty Images(SAN DIEGO) -- Peter Robbins, who provided the voice of Charlie Brown in several 1960s animated Peanuts TV specials, pleaded not guilty Wednesday in a San Diego court to 12 felony counts of making criminal threats and stalking.

The 56-year-old is charged with stalking his ex-girlfriend Shawna Kern and making criminal threats against Dr. Lori Saltz, a La Jolla, Calif., plastic surgeon who reportedly performed breast augmentation surgery on Kern.

Robbins was arrested last weekend. Bail has been set at $550,000. If convicted, he faces up to nine years in state prison.

San Diego County Deputy District Attorney Elizabeth McClatchy said on Wednesday that Robbins has been "acting erratically" and has, "used physical violence against one of the victims and against his dog."